1. Field of the Invention
The present invention relates to a method for monitoring tyre deformations and to a corresponding monitoring system.
2. Description of the Related Art
As it is known, tyre deformations are induced by the interplay of lateral or longitudinal forces produced by the motion itself of a motor vehicle and friction of tyres with the road. Deformations represent a viable way for monitoring, relevant parameter such, as slipping angles, flattening and, generally speaking, variations in the footprint area of a tyre, which control the adhesion and friction of a tyre with the road. In turn, such detected information can be useful to prevent critical situations; thus improving the whole safety level of vehicles.
A number of different systems and methods have been proposed for measuring the tyre deformations. These methods are based upon direct measures of twisting forces or upon coupling of suitable signal generators with sensors capable to measure these signals.
Among them, magnetic systems (see, for instance; EP 1 289 813, and U.S. Pat. No. 5,964,265) have been proposed.
EP 1 289 813 (in the Applicant's name) discloses a system for monitoring the shear deformations of a crown portion of a tyre during the running of a motor vehicle. It comprises at least one magnetic field (hereinafter also referred to as MF) generator, preferably a strip of magnetic material applied to the tyre, and at least a sensor strip measuring the MF variations of said MF generator. Each magnetic generator generates a magnetic field of intensity which is detected by the corresponding magnetic induction sensor. The monitoring of the tyre deformations is effected by measuring the variation in time of the magnetic field produced by the MF generator during the running.
U.S. Pat. No. 5,964,265 (in the name of Continental Aktiengesellschaft) discloses a system for determining tyre-road adhesion. The system is composed by a subsystem, for generating data comprising a magnetic sensor and a magnetic field produced by partial magnetization of the belt in radial direction. Such belts can contain ferromagnetic powders to increase the MF produced. The sensors are, placed within the tread.
U.S. Pat. No. 6,404,182 (in the name of Canon Denshi) discloses a system for detecting the revolution of tyres using a magnetic field. In an embodiment the tyre steel belts performs as MF generator, being, uniformly magnetized in a direction for a portion, of the circumference and in the opposite direction for the other portion of the circumference. Another embodiment consists in providing a magnetic member inside the wheel. The magnetic field generated, for example, by the magnetized steel belt is detected by two magnetic detection elements, which are set so that the magnetic field detection directions of the twos magnetic detection elements are parallel to the side surface of the tire, and the two elements are juxtaposed in a direction perpendicular to the side surface of the tire. Said detection elements are provided in the vicinity of the tyre, in a fixed position, for example on the side of a seat.
U.S. Pat. No. 5,670,877 (in the name of Hughes Electronics) discloses a method and apparatus for sensing rotation of shafts. It comprises two magnetic sensors disposed with respect to a rotating magnetic source, which is integral with the shaft itself, to sense the MF components, that are generated. The magnetic generator is a magnet positioned along a part of the shaft with a north and south pole. Under rotation of the shaft a waveform signal is produced with a periodically variable magnetic field. Measuring the period of revolution and the variation of these periods results in information on the acceleration and velocity during the shaft revolution. Possible applications are ABS systems.
The systems disclosed by the above mentioned documents provide partial information about the deformation of a tyre.
In the case of U.S. Pat. No. 6,404,182 and U.S. Pat. No. 5,964,265 the magnetization of the steel belt of the tyre can provide information about deformation just in running conditions. Analogous consideration may be applied to U.S. Pat. No. 5,670,877.
Also in the case of EP 1 289 813 the information collected is not satisfactory. The system therein disclosed is based on MF generator/sensor units operating independently from one another, i.e. each sensor detects MF variation from a single generator. This results in a mono-dimensional, reading of the magnetic field because only the intensity modulus, is measured.